Five main categories of experiments were described in the initial proposal. Of these, one (solubility of deoxyhemoglobin S, in mixtures with other hemoglobins and with liganded forms) is within sight of completion. Experiments are still needed with (a) hemoglobin F, the foetal human form, which is well known to differ qualitatively from other mutants, (b) cyan methemoglobin F which is reported to be aggregatable, and (c) cyan met itself which is complicated by an unusual dependence of much of its behavior on pH. We have also entered on a program that will distinguish between the aggregation in mixtures of hybrid and non-hybrid tetrameric starting material. This constitutes the second category. The third category, already well under way, uses the delay time in onset of gelling (essentially under low shear) to follow the kinetic aspects of the aggregation process. Excellent new equipment is already yielding very reproducible delay times as systematic functions of composition and concentration of mixtures of deoxy sickle hemoglobin with other forms. Simple interchange equivalences have been found at concentrations that are not too far above the mgc, but they become more complicated at higher very non-ideal concentrations. A beginning has been made on following the kinetics of gelation by means of the relaxation of electrical birefringence; deducing both conformation change and viscosity from the kinetics of rotational diffusion. The reversibility seems to be imperfect in our experiments so far. Experiments with intact sickle erythrocytes, as affected by changes in hemoglobin species (observed by visual inspection under the microscope) and induced by various permeating agents are to begin soon. Some of the proposed experiments were described in the original Proposal.